The invention concerns an asymmetrical bipolar voltage supply having a transformer with at least one primary winding and a plurality of secondary windings, and a primary-side power supply connected to the transformer.
Modern power semiconductors that are to be used as semiconductor switches require an asymmetrical bipolar voltage supply of, for example, +15 and −5 volts for gate control. This is to prevent faulty switching. Such faulty switching can occur if the gate control is only set to zero potential in order to reach a switching state, and an interference is superimposed on this zero potential. In such a case, the semiconductor switch may begin to oscillate, which would quickly lead to its destruction. If, however, a voltage of −5 volts is applied, an interference cannot hinder the proper operation.
To control the semiconductor switches of a full-bridge (also referred to as an H-bridge), four gate drivers are required with the technology customary today, wherein each gate driver is connected to one asymmetrical bipolar voltage source. In a modern three-phase power supply with Power Factor Correction (PFC) and downstream full-bridge voltage converter, six semiconductor switches are required for the PFC and four semiconductor switches for the downstream full-bridge voltage converter. Thus, ten gate drivers with the associated asymmetrical bipolar voltage sources are required. A regenerative variable frequency drive requires even at least twelve gate drivers with the above-mentioned asymmetrical bipolar voltage sources.
Usually, a transformer that has a corresponding number of secondary windings is used for the design of such a voltage source. A separate winding is required for the positive and the negative voltage, respectively, wherein the positive and the negative windings can have a common ground point. The output voltages are set via the turn ratio of primary and secondary windings.
This means that two secondary windings have to be provided for each gate driver. Thus, in the above-mentioned full-bridge circuit, eight secondary windings are required and even twenty secondary windings are required in the above-mentioned three-phase power supply.
This large number of secondary windings leads to an overall design size with the associated high parasitic capacitances. These parasitic capacitances can lead to disturbances, which are caused by leakage currents and, in the worst case, will lead to a destruction of the voltage supply or the gate driver.